Various sewing machines capable of sewing desired embroidery patterns on a workpiece set in an embroidery frame by mounting an embroidery device in an electronic sewing machine capable of sewing utility patterns such as zigzag stitches and triple stitches, and common patterns including various ornamental patterns have been commercialized and proposed. Recent electronic sewing machines are being provided with a workpiece feeding distance modifying motor for modifying the tilt of a feeding regulator in a feed dog driving mechanism fox driving the feed dog to move a workpiece; a needle swing motor for driving a needle swinging mechanism to pivot a needle bar; a frame moving motor built into the embroidery device for driving the embroidery frame in two directions orthogonal to one another (X- and Y-directions); and the like.
For example, a sewing machine described in Japanese unexamined patent application publication No. HEI-11-164976 includes a needle bar driving mechanism for driving the needle bar vertically; a needle bar swinging mechanism for swinging the needle bar; a thread take-up driving mechanism for driving the thread take-up; a forward/rearward feed dog driving mechanism for driving the feed dog forward and rearward; and the like. The sewing machine also includes a stepping motor for driving the needle bar swinging mechanism; a stepping motor for driving the forward/rearward feed dog moving mechanism; a stepping motor for driving a left/right driving mechanism provided in the embroidery device; and a stepping motor for driving a forward/rearward driving mechanism.
In order to drive the stepping motors with this construction, a driver circuit for each stepping motor is necessary for supplying a drive current to an excitation coil. Further, a plurality of input/output ports and the like are required in a control device for supplying an excitation signal comprising a step pulse to each driver circuit.
A sewing machine capable of sewing embroidery patterns according to Japanese unexamined patent application publication No. HEI-11-164976 described above is provided with stepping motors for swinging the needle bar and for driving the feed dog, and the embroidery device is provided with stepping motors for moving the embroidery frame left and right and forward and rearward. Hence, not only are a plurality of driver circuits required for driving each of the stepping motors, but the CPU in the controller requires 4-8 input/output ports for these stepping motors according to the number of excitation phases.
Recent computerized sewing machines equipped with numerous functions include not only the stepping motors described above, but also numerous stepping motors for an automatic thread guard mechanism, automatic thread adjusting mechanism, electronic thread cutting mechanism, automatic threading mechanism, thread winding mechanism, and the like. As the number of stepping motors increases, not only does the number of driver circuits increase, but also does the number of input/output ports required in the CPU for connecting the CPU to these driver circuits.
A CPU having a large number of input/output ports is generally more expensive than a CPU with few ports, leading to an increase in the cost of the sewing machine. Further, since a CPU with a large number of input/output ports is generally larger in size, the circuit board on which this large CPU is mounted is also larger in size, leading to an increased size of the sewing machine.
Further, since the operating properties of these driving mechanisms differ according to each use, the magnitude of the torque for driving the driving mechanisms also differs. As a result, since the drive currents supplied to the stepping motors for driving the driving mechanisms differ, a universal driver circuit cannot be used to drive all the stepping motors.
While it is conceivable to connect an ASIC (Application Specific Integrated Circuit), and particularly gate array IC chips, to the input/output ports of the CPU to reduce the number of required I/O ports, these gate array IC chips are configured of LSI chips manufactured individually according to specification and are therefore more expensive.